High modulus asphalt concrete mainly adopts low labeled hard asphalt as the cementing material, the characteristics of high viscosity, high stiffness and low temperature sensitivity of low labeled hard asphalt provides excellent high temperature stability and high modulus value to the asphalt mixture, it can improve the pavement anti-rutting ability and have certain structure reinforcing effect, and also can prolong the service life of road and thinning thickness of road surface, reduce the cost when it is used as middle and lower layer of the asphalt pavement.
High modulus asphalt concrete is mainly applied in some developed countries in Europe. It is early studied and the most widely used in French, there the technology is mature, Other countries such as Britain, Finland and so on mainly reference the experience of France's achievements and carry out related research and application. Currently, the main design method of high modulus asphalt concrete abroad is the maximum nominal size is not more than 19 mm, using low grade asphalt with low penetration and continuous gradation, the asphalt mixture designed have higher asphalt content and low void ratio, the increasing of the mix modulus is mainly from the quality of the asphalt itself, and by increasing the dosage of asphalt to improve the compactness of asphalt mixture and the ability to resist fatigue.
But for heavy traffic asphalt pavement and long-life asphalt pavement design, the key problem is to improve the bearing capacity of pavement structure and ensure the high temperature stability of the surface, especially for the middle and lower layer, material not only to provide good ability to anti-rutting, also requires a certain structure reinforcing effect. Because the design method of high modulus asphalt concrete abroad is not applicable to coarse grain type of the nominal maximum aggregate size greater than 19 mm, and its design idea is to choose continuous gradation and higher binder dosage, the air void of asphalt mixture designed is low, which is not applicable to the case of heavy traffic. Therefore, inventing a kind of mix composition determination method of coarse graded high modulus asphalt concrete with skeleton embedded structure is very necessary.
Invention Content
The aim of the present invention is to meet the construction need of long-life and durable asphalt pavement, put forward a kind of new coarse graded high modulus asphalt concrete with skeleton embedded structure which is technology reliable and economy reasonable, this kind of asphalt mixture has good high temperature stability and bearing capacity, its strength is 50% higher than that of the general asphalt mixture, its dynamic complex modulus is 30% higher than that of similar foreign products, it has very excellent road performance, can be used as the material of middle and lower layer of overloading traffic long-life asphalt pavement, and reduce the project cost.
Mix composition determination method of coarse graded high modulus asphalt concrete with skeleton embedded structure includes the following steps: 1, the preparation of raw materials, 2, determine the design curve, 3, determine the optimum proportion.
For step 1, choosing low labeled hard asphalt with penetration degree of no higher than 30 as the cementing material, choosing coarse aggregate, fine aggregate and mineral powder, the maximum nominal size of the coarse aggregate is no smaller than 26.5 mm.
Step 2 including the following steps: (1), according to the need of designation, determine the maximum nominal size of coarse graded asphalt concrete and the aggregate passing rate of the three key meshes, cut-off point of coarse aggregate and fine aggregate 4.75 mm and 0.075 mm, (2), using formula 1 the maximum nominal size determined and the aggregate passing rate of the two key meshes of 4.75 mm, calculate coefficient A and B, determine the specific expression of the formula 1; using formula 2 the aggregate passing rate of the two key meshes of 4.75 mm and 0.075 mm, calculate coefficient C and D, determine the specific expression of the formula 2.P.sub.di=A(d.sub.i).sup.B  (formula 1)
Pdi—Passing rate of coarse aggregate sieve size di, %;
di—sieve size of coarse aggregate, mm
A, B—coefficientPdj=C(dj)D  (formula 2)
Pdj—Passing rate of fine aggregate sieve size di, %;
dj—sieve size of fine aggregate, mm
C, D—coefficient
(3), calculate the passing rate of each sieve between the maximum nominal size and 4.75 mm by formula 1; calculate the passing rate of each sieve between 4.75 mm and 0.075 mm by formula 2, then get the design grading curve of coarse graded high modulus asphalt concrete with skeleton embedded structure.
Step 3 including the following steps: A) choosing 5˜6 oil-stone ratios that interval is 0.3%˜0.4% according to the grading curve designed in step 2, forming 4˜6 specimens under each oil-stone ratio, determining the gross volume density and the theoretical maximum density of the specimens.
B), calculate the dry density of the mix, voids in mineral aggregate VMA and voids in coarse aggregate VCA, draw the quadratic curve between dry density, VMA, VCA and oil-stone ratio respectively, select the average of the oil-stone ratio OAC1 corresponds to the minimum value of VMA, the oil-stone ratio OAC2 corresponds to the minimum value of VCA and the oil-stone ratio OAC3 corresponds to the maximum value of dry density of the mix as the optimum oil-stone ratio OAC of coarse graded high modulus asphalt concrete with skeleton embedded structure, that is: OAC=(OAC1+OAC2+OAC3)/3.
The low labeled hard asphalt is AH-30#.
The maximum nominal size of coarse aggregate is 26.5 mm.
The gross volume density of the specimen is measured by wax sealing method.
The theoretical maximum density of the specimen is measured by vacuum method.
The mix designed by the method above including asphalt, coarse aggregate, fine aggregate and mineral powder, the design gradation curve and the optimum oil-stone ratio.
Coarse graded high modulus asphalt concrete with skeleton embedded structure designed in this invention is made up of low labeled hard asphalt AH-30# with penetration is about 30 (0.1 mm), coarse aggregate of the maximum nominal size no smaller than 26.5 mm, fine aggregate and mineral power.
This invention including the following steps:
1, Choose the domestic low-labeled hard asphalt with penetration no higher than 30 (0.1 mm) as the cementing material of high modulus asphalt concrete, usually adopt modified asphalt, natural bitumen (lake asphalt, rock asphalt), adjusting agent, which not only saves the project cost, and easy to project operation and quality control.
2, choose Coarse aggregate with maximum nominal size is not less than 26.5 mm, the coarse aggregate, fine aggregate and mineral powder used should be consistent with the requirements of the technical specification for construction of highway asphalt pavement (JTG F40-2004), this is different from the technical requirements of high modulus asphalt concrete with the nominal maximum particle size is not more than 19 mm abroad.Building mineral aggregate gradation of the mix by the idea of course aggregate gap gradation is completely different from the gradation composition method of high modulus asphalt concrete home and abroad.
(1), according to the need of designation, determine the aggregate passing rate of the three key meshes, cut-off point of coarse aggregate and fine aggregate 4.75 mm and 0.075 mm.
(2), using formula 1 the maximum nominal size can be determined and the aggregate passing rate of the two key meshes of 4.75 mm, calculate coefficient A and B, determine the specific expression of the formula 1; using formula 2 with the aggregate passing rate of the two key meshes of 4.75 mm and 0.075 mm, calculate coefficient C and D, determine the specific expression of the formula 2.Pdi=A(di)B  (formula 1)
Pdi—Passing rate of coarse aggregate sieve size di, %;
di—sieve size of coarse aggregate, mm
A, B—coefficientPdj=C(dj)D  (formula 2)
Pdj—Passing rate of fine aggregate sieve size di, %;
dj—sieve size of fine aggregate, mm
C, D—coefficient
(3), calculate the passing rate of each sieve between the maximum nominal size and 4.75 mm by formula 1; calculate the passing rate of each sieve between 4.75 mm and 0.075 mm by formula 2, then get the design grading curve of coarse graded high modulus asphalt concrete with skeleton embedded structure.
4. Using gradation design method of asphalt mixture based on closest compact condition to select the optimal oil-stone ratio of coarse graded high modulus asphalt concrete with skeleton embedded structure, which is the core of the patent invention, is not only different from the optimal oil-stone ratio selecting method by asphalt film thickness abroad, and also different from the optimal oil-stone ratio selecting method by the designed porosity 4%.
(1) For the grading curve designed in step 3, choose 5˜6 oil-stone ratios that interval is 0.3%˜0.4% according to the experience, forming 4˜6 specimens under each oil-stone ratio, determining the gross volume density and the theoretical maximum density of the specimens.
(2) calculate the dry density of the mix, voids in mineral aggregate VMA and voids in coarse aggregate VCA, draw the quadratic curve between dry density, VMA, VCA and oil-stone ratio respectively, select the average of the oil-stone ratio OAC1 corresponds to the minimum value of VMA, the oil-stone ratio OAC2 corresponds to the minimum value of VCA and the oil-stone ratio OAC3 corresponds to the maximum value of dry density of the mix as the optimum oil-stone ratio OAC of coarse graded high modulus asphalt concrete with skeleton embedded structure, that is: OAC=(OAC1+OAC2+OAC3)/3.
5. Using the optimum oil-stone ratio of coarse graded high modulus asphalt concrete with skeleton embedded structure determined in step 4 to assess the road performance index high temperature properties, strength and modulus, fatigue performance and so on. Confirm the mixture has good high temperature stability and excellent mechanical strength, modulus and fatigue life through laboratory test and actual engineering verification.
Coarse graded high modulus asphalt concrete designed and prepared by this method, because of the adoption of AH-30# low-labeled hard asphalt as a cementing material, the choosing of coarse grain type with the maximum nominal size no less than 26.5 mm, the using of the idea of course aggregate gap gradation to building mineral aggregate gradation of the mix and gradation design method of asphalt mixture based on closest compact condition to select the optimal oil-stone ratio of asphalt concrete, so that the high modulus asphalt concrete can form the most closely skeleton embedded structure, and significantly improve the high-temperature stability of asphalt mixture, while improving the modulus of asphalt mixture more than 30%, and reduce the project cost, which can be used as the material of middle and lower layer of overloading traffic long-life asphalt pavement.